A conventional crown portion 40 for bicycles is disclosed in FIGS. 7 and 8, and generally includes a first tube 42 defined in a center thereof so that a steerer tube of a front fork (both not shown) extends through the first tube 42, and two arms 41 are connected to the first tube 42. Each arm 41 has a second tube 43 connected to a distal end thereof so that two leg portions (not shown) of the front fork extend through the two first tubes 42. It is noted that the arms 41 are solid and complained by the users of their weight. Another crown portion is disclosed in FIG. 9 and a hole is drilled from outside of the second tubes 43 on the two arms 41 and extended to the first tube 42. The hole defines an opening 46 in the outside of each of the second tubes 43 and a through hole 47 is defined in communication between the first and second tubes 42, 43. A positioning plate 48 has to be put in the conjunction of each arm 41 and each second tube 43 to position the leg portions 49 extending through the second tubes 43. The positioning plates 48 are fixed by two bolts 481 which extend through the arms 41 and are connected to the positioning plates 48. There are several shortcomings in the conventional crown portion. Firstly, the openings 46 in the second tubes 43 weaken the structural strength of the second tubes 43 and the manufacturers have to cover the openings 46 by extra processes. Secondly, the arms 41 have to be further drilled with a hole for the bolts 481 to extend and the holes for the bolts 481 often crack during severe actions of the bicycles. Thirdly, it takes a lot of time to put the positioning plates 48 in the second tubes 43.
The present invention intends to provide a crown portion for bicycles wherein the arms includes at least two passages which are in communication between the first and second tubes so that the weight of the crown portion is reduced while the structural strength is maintained.